1. Field of the Invention
The present invention relates to a method for producing a bridged type transition metal complex. More particularly, it relates to a method for producing a bridged type transition metal complex having one group with a cyclopentadiene anion skeleton, which is useful as a catalyst component for olefin polymerization.
2. Description of the Related Arts
Transition metal complexes having a group (Cp) with a cyclopentadiene anion skeleton are effective as a catalyst for various organic synthesis reactions, and have widely used and studied at present. Among them, a complex containing an early transition metal such as titanium and zirconium is efficient as a catalyst component for olefin polymerization, and its study including practical use has widely been studied.
Particularly, WO9308199 and U.S. Pat. No. 5,096,867 disclose that a catalyst for olefin polymerization comprising, as a main component, a bridged type mono-Cp complex represented by the following structural formula, such as dimethylsilylene(tetramethylcyclopentadienyl) (tert-butylamide)titanium dichloride shows high activity. However, it is generally difficult to produce such a complex having a complicated structure, and the difficulty of the production was an obstacle in case of using the complex industrially. ##STR1##
As the method of producing such a bridged type mono-Cp complex, particularly dimethylsilylene (tetramethylcyclopentadienyl)(tert-butylamide)titanium dichloride [Me.sub.2 Si(C.sub.5 Me.sub.4)(NtBu)TiCl.sub.2 ], JP-A-07-053618, JP-A-05-505593 and EP-A-601830 disclose a method of reacting a diethyl ether or tetrahydrofuran complex of titanium tetrachloride, which is prepared in the system under freezing at low temperature or separately synthesized and isolated, with [Me.sub.2 Si(C.sub.5 Me.sub.4)(NtBu)]Li.sub.2, which is separately synthesized and isolated from [Me.sub.2 Si(C.sub.5 Me.sub.4 H)(NHtBu)], in tetrahydrofuran or diethyl ether at low temperature.
However, this method has a problem that the yield of the desired complex is low and that it is difficult to handle [Me.sub.2 Si(C.sub.5 Me.sub.4)(NtBu)]Li.sub.2 isolated as a intermediate because it is considerably sensitive to moisture and oxygen in the air and has flammable.
In this method, a solvent such as diethyl ether, tetrahydrofuran or the like, is used to enhance the solubility of a lithium salt compound as the intermediate. Therefore, it was necessary that a complex of titanium tetrachloride with diethyl ether or tetrahydrofuran was previously prepared. Such a complex-forming reaction is a vigorous exothermic reaction and is normally carried out under freezing at low temperature, and should be avoided in the industrial production. Besides, the solubility of the complex thus obtained in diethyl ether or tetrahydrofuran is not sufficiently high. Moreover, since salts produced as by-products after the reaction, such as LiCl, etc. are soluble in these solvents, it is sometimes difficult to remove them by filtration. When a trial for obtaining the desired product by crystallization without removing these salts is made, a mixture of the desired product and the salts is sometimes obtained. Therefore, it is necessary to separate the desired product from the salts by a method of evaporating the solvent from the reaction solution, followed by solvent replacement with an aliphatic hydrocarbon solvent, an aromatic hydrocarbon solvent, etc. So, the synthesis method still has a problem to be solved in view of efficiency.
In addition, JP-A-07-053618, JP-A-05-230123 and EP-A-639579 disclose a method of reacting a tetrahydrofuran complex of titanium trichloride with the above lithium salt compound or a magnesium salt compound, [Me.sub.2 Si(C.sub.5 Me.sub.4)(NtBu)](MgCl).sub.2 (THF), which has been separately synthesized and isolated by the reaction between [Me.sub.2 Si(C.sub.5 Me.sub.4 H)(NHt-Bu)] and a Grignard reagent (i-PrMgCl), and oxidation-treating the reaction product with a small amount of dichloromethane, carbon tetrachloride, decyl chloride or silver chloride.
Furthermore, WO95/19984 discloses a method of synthesizing the desired complex by reacting a tetraalkoxytitanium with the above magnesium salt compound and treating the reaction product with silicon tetrachloride, boron trichloride or diethylaluminum chloride.
However, with respect to these methods, it could not be said that the yield is sufficiently high. Also, the following problems still remain. That is, when the number of steps is large or the reaction is performed via a lithium salt compound, there arises the same problem as that is described above. When a Grignard reagent is used, the yield of the magnesium salt compound as an intermediate is not sufficient (about 65%) and an isolating operation is required. Since the ether solvent is used, there is required a step of separating LiCl, MgCl.sub.2, etc. formed as by-products after the reaction by using a method of solvent replacement.
Generally, in the construction of an industrial production process, the isolation of the intermediate can be omitted and the reaction at low temperature near -78 or -40.degree. C. should be avoided because of causing the limitation of using used materials for the device and a high cost for equipment such as coolant. Furthermore, a method of producing the product efficiently in a short time using as little solvent replacement as possible is preferable. As described above, conventional methods showed insufficient yield and still had various problems to be solved in the case of carrying out the method on an industrial scale.